The present invention relates to improvements to the utility, efficiency, ecology, safety, and cost of prime mover dynamos that extract useful renewable power from a stream of water or wind. More specifically, this invention improves on the class of dynamos that do not rely on complex adjustment mechanisms or precise airfoil sections.
There are several types of wind and water dynamos known to those versed in the art:
Many vertical and horizontal wind and water dynamos use airfoil shaped blades and or stators that are difficult and expensive to manufacture, and maintain. They are subject to over speed, and sudden destructive failure modes that make them dangerous. A blade failure can send a heavy blade flying to the ground, and may even bring the whole tower down. Many also require complex gear boxes, and blade pitch control. The horizontal axis wind dynamo types must be built on tall towers, and the driven device is difficult to service, and bird kill is a problem. Many horizontal axis wind dynamos that use propeller type rotors have no way to stop the rotor for repair in high wind without risking rotor destruction.
One dynamo type is well known as the xe2x80x9cSavonius rotorxe2x80x9d, as taught by U.S. Pat. No. 1,697,574 issued to Savonius, Jan. 1, 1929. The Savonius rotor type uses a pair of concave vertical sheets placed parallel to a vertical axis such that they rotate and produce usable power, in response to a fluid moving perpendicular to the axis of rotation. The Savonius rotor type dynamos are not as efficient as dynamos that use airfoil shapes to extract energy from a fluid stream, but they are much easer to build, and do not require expensive tooling or complex molds, or complex mechanisms of operation.
In Operation the Savonius Type Dynamos Have Several Problems
Low starting torque.
Inability to self start at times depending on wind direction; if the wind direction is aligned with the rotors zero torque angle, the rotor may not self start.
Rotational speed and torque fluctuations; there is a torque pulse each revolution, as each blade rotates through the moving fluid and extracts energy from it.
Over speed in high wind can cause structural or electrical damage.
Insufficient rotational velocity for direct drive electricity generation in low and moderate wind.
Poor efficiency; only about 30% of the energy is captured, partly due to the fact that the moving fluid strikes the back side of the advancing blade.
Noisy operation due to the pressure pulses induced by only 2 power strokes per revolution.
Structural weakness; the two blades are roughly in the same plane so the rotor design is not as stable to forces normal to that plane.
The blade elements are large and cannot be easily broken down to transportxe2x80x94especially for large machines.
Others have attempted to correct the deficiencies of the Savonius type dynamos with limited success, and often added complication:
U.S. Pat. No. 6,428,275, Aug. 6, 2002, to Jaakkola discloses the use of a twisted blade to address the torque variation problem of Savonius; but the rotors require specialized equipment to form, and fluid flow tends to follow the direction of the spiral and passes without performing as much work. The helical blade elements are large and difficult to work with. The torque pulse travels linearly down the blade elements, and may develop tensional resonance if the rotational frequency corresponds with the natural torsional frequency of the rotor. The long open shapes contribute to reduced torsion rigidity.
U.S. Pat. No. 6,345,957, Feb. 12, 2002, to Szpur discloses a variation on the shape of the rotor members, and a means for controlling airflow through the rotor to limit speed in high wind. The suggested arrangement adds expense and complication of spring loaded baffle devices to limit speed, this may compromise reliability and increase maintenance requirements. The improvement over Savonius is minimal if any.
U.S. Pat. No. 6,283,711, Sep. 4, 2001, to Borg et al. discloses a variation on the shape of the rotor, and hinging a portion of the rotor blades to change shape in response to centrifugal forces of rotation. The added complexity compromises reliability and maintenance. The hinged free ends of the blades impose high forces, and must be of heavy construction to resist damage. The balance of the machine could be catastrophically affected if one side should fail to deploy at the same rate as the other side.
Both Szpur, and Borg fail to address the problems of: noise; and torque/velocity variations of the rotor; and moving fluid striking the back side of the advancing blade.
U.S. Pat. No. 6,242,818, Jun. 5, 2001, to Smedley discloses a dynamo with a multiplicity of hinged surfaces that respond to variations in wind pressure and centrifugal force to limit speed in high wind. This has the disadvantages of Borg, and has many more moving parts and consequently more opportunity for wear and failure. The stress on the parts is also much higher, as all force exerted on the movable elements must be transferred through the hinge pins.
U.S. Pat. No. 5,494,407, Feb. 27, 1996, to Benesh; discloses a modification of the blade shape to enhance energy capture efficiency. The design fails to address the other flaws of the Savonius type dynano.
U.S. Pat. No. 5,391,926, Feb. 21, 1995, to Staley et al discloses a three lobed rotor with fixed stators to direct fluid through the dynamo. The invention fails to address the rotational speed and torque fluctuations of the rotor. The projected area of the stators is much greater than the projected area of the rotor, resulting in less power for a given foot print. The turbine is designed to work best in high winds, but there are few populated areas with consistently high wind velocity.
U.S. Pat. No. 4,784,568 Nov. 15, 1988, to Benesh discloses a Savonius type dynamo with a deflector to assist starting, and to increase torque. The deflector substantially increases the footprint of the dynamo, since it needs radial clearance to move to remain in alignment with the fluid flow.
U.S. Pat. No. 4,293,274 Oct. 6, 1981, to Gilman discloses a helically twisted blade element to overcome torque variations. Like Jaakkola, the blade elements are bulky and difficult to manufacture. Gilman""s device is also very complex, with many moving parts to regulate speed.
Rotary electrical generation devices are a highly developed field. Many types are well known to those versed in the art. Generally speaking, electrical generating equipment is lower cost, and takes fewer materials to produce a given amount of power if the generating elements can operate at high relative velocity. This high velocity is normally obtained by large diameter, or high rotational rate.
Rotational anti friction bearings that use magnetic force for radial and axial constraint are known to those versed in the art.
I, the inventor of the present invention, George Sikes received a U.S. design Pat. No. 300,932 Dated May 2, 1989, for a windmill design that when built, tested, and optimized eventually developed into to the present invention, the subject of this disclosure.
The present invention seeks to exploit many advantages of the listed prior art dynamo technologies that extract power from a moving fluid, while reducing the disadvantages. The dynamo of this invention can be applied to both horizontal and vertical axis applications as will be apparent to those versed in the arts, and according to the following descriptions. The objects are:
Simplified construction using low cost, light weight materials, and smaller built up parts that may be mass produced, with low waste.
Increased starting torque and efficiency
Smooth power delivery without torque variation.
Means to adjust the torsion timing sequence of power pulses.
Simple mechanisms with low maintenance requirements.
Rigid structure to withstand storm conditions.
Optional compact deflector that takes little extra space, and increases energy capture by extracting fluid from the advancing side of the rotor.
Small foot print, with safe operation in populated areas.
Simple rotor speed control, and stopping means with optional deflector.
Means for either direct drive counter-rotation electrical generation equipment, or speed step-up (or step-down) drive for PTO.
Means to maintain rotor balance for vibration free operation.
Less noise due to flow interruptions.
Low cost, low tech production methods.
Many more advantages will be apparent upon inspection of the detailed description of preferred embodiments by those who know the various arts employed.